1. Field of the Invention
The present invention relates to a valve configured to control excess flow of fluid in a forward direction and a fuel cell system including the valve.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2008-59093 discloses a passive drive-type pressure reducing valve that is used for a small-sized fuel cell. The pressure reducing valve is configured such that when a pressure of fluid reaches a set pressure, the valve is opened or closed automatically using pressure difference.
FIG. 9A and FIG. 9B illustrate cross-sectional views of the pressure reducing valve disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093. The pressure reducing valve is constituted by a diaphragm 1 serving as a movable portion, a piston 2 serving as a transmission mechanism, a valve seat portion 3, and a valve body portion 4 and a supporting portion 5 forming a valve portion. The valve body portion 4 is supported by the supporting portion 5 with respect to surrounding portions, and abuts against the valve seat portion 3 in a valve closed state (see FIG. 9A). The supporting portion 5 is formed by an elastic beam.
The respective members are configured by plate-shaped members and the pressure reducing valve is formed by bonding the respective members. A peripheral edge portion of the diaphragm 1 is held between a valve housing 7 and a cap 8, and the valve housing 7 configures a valve chamber 6 together with the diaphragm 1.
It is assumed that a pressure of an upper portion of the diaphragm 1 is P0, a primary pressure of a valve upstream portion is P1, a pressure of a valve downstream portion is P2, an area of the valve body portion 4 is S1, and an area of a portion of the diaphragm 1 which contacts with the valve chamber 6 (hereinafter, referred to as a pressure receiving area) is S2. In this case, a condition under which the valve is opened is represented by (P1−P2)S1<(P0−P2)S2 based on pressure balance. When P2 is higher than the pressure satisfying the condition, the valve is closed; when P2 is lower than that, the valve is opened. This enables P2 to be kept constant.
For example, a direct methanol fuel cell (DMFC) includes a pump that transports liquid fuel (methanol) to a power generation cell (at the downstream side of the pump) from a fuel cartridge (at the upstream side of the pump). When the pump uses a valve system, the pump has a check function for blocking flow of the fluid to the upstream side of the pump from the downstream side of the pump, with a valve. However, the pump does not generally have a function for blocking excess flow of the liquid fuel from the upstream side of the pump to the downstream side of the pump, that is, a forward check function.
For example, in a direct methanol fuel cell system, a fuel cartridge that is incorporated in the fuel cell system is heated to a high temperature due to a heating component in some cases. When the fuel cartridge is heated to a high temperature, the liquid fuel in the fuel cartridge expands. Therefore, a high-pressure liquid fuel may be discharged from the fuel cartridge in some cases. Accordingly, with the pump of the valve system which does not have the forward check function, an excess amount of liquid fuel is supplied to the power generation cell so that the liquid fuel is transported from the fuel cartridge to the power generation cell undesirably even in a state of non-operating the pump. Further, the pump may be broken in some cases.
In order to solve the problem, it is desired that such a valve stops the flow in the forward direction when, for example, a high-pressure liquid fuel is applied. The inventors of the present application have discovered that such a valve stops the flow in the forward direction when, for example, a high-pressure liquid fuel is applied and that is opened and closed with pressure of the pump is provided between the fuel cartridge and the pump. In the pressure reducing valve in Japanese Unexamined Patent Application Publication No. 2008-59093 as illustrated in FIG. 9A, the diaphragm 1 is made of rubber, for example. In order to ensure a sealing property of the valve chamber 6, a method in which both main surfaces of the peripheral edge portion of the diaphragm 1 are pressed is generally used. In the pressure reducing valve in Japanese Unexamined Patent Application Publication No. 2008-59093, the peripheral edge portion of the diaphragm 1 is held between the valve housing 7 and the cap 8.
In the pressure reducing valve described in Japanese Unexamined Patent Application Publication No. 2008-59093, however, there has been a problem that when the peripheral edge portion of the diaphragm 1 is pressed, the diaphragm 1 is bent and the piston 2 is displaced to the valve body portion 4 side. In the pressure reducing valve described in Japanese Unexamined Patent Application Publication No. 2008-59093, as illustrated in FIG. 9B, there is a risk that the piston 2 pushes down the valve body portion 4 and, at worst, may open the valve unintentionally in the state of non-operating the pump.